In the manufacture of glyphosate (N-phosphonyl methyl glycine), the acid form is precipitated from the reaction mixture and the resulting wet cake is reacted with an appropriate base to form a water soluble salt. The intermediate technical grade glyphosate free acid is poorly water soluble and is not used as a herbicide. The herbicidal composition of salts of glyphosate is then prepared from the salt as an aqueous solution concentrate and may contain adjuvants such as surfactants that reinforce the herbicidal effect of glyphosate.
There is an ongoing need to provide solid glyphosate formulations that contain higher levels of glyphosate on an acid equivalent (ae) basis—this is because such formulations are more convenient for the farmer to use, require less packaging to deliver and provide a means of achieving product differentiation.
Some highly loaded fully formulated solid glyphosate compositions that have been developed include the following:                U.S. Pat. No. 5,633,397 (Gillespie et al., filed 1995) describes the preparation of mono-ammonium glyphosate via a gas-solid reaction system. The reaction product dissolves readily and completely in water and can be used to prepare a highly-loaded, adjuvant-containing (ie fully formulated) glyphosate composition. The maximum glyphosate loading in a fully formulated solid glyphosate composition in this patent (example 2) comprises 80% mono-ammonium glyphosate, which corresponds to 72.5% glyphosate acid equivalent (ae). This patent describes prior art related to the preparation of glyphosate salts, including U.S. Pat. No. 5,047,079 (isopropylamine salt), U.S. Pat. No. 5,070,197 (sodium salt), U.S. Pat. No. 5,266,553 (ammonia, alkylamine, hydroxylamine, alkali metal salts).        US application 20080194409 (Bernadini et al., filed 2006) describes a process for preparing mono-ammonium glyphosate salt wherein a Broensted base which supplies ammonium ions is added to glyphosate acid. Tight control is required over reaction conditions. This application notes that mono-sodium and mono-ammonium glyphosate salts are particularly suitable for making water-soluble glyphosate granules, and that the ammonium salt is particularly suitable as it is less hygroscopic, and thus more storage stable. This application notes that handling ammonia can be challenging with respect to corrosive hazard, gas containment and/or thermal hazard associated with the neutralisation exotherm. Examples 1, 2 and 3 in this application describe fully formulated glyphosate compositions having a glyphosate loading of 72% ae by weight—this is the maximum glyphosate ae loading achieved.        WO 92/12,637 describes a process wherein glyphosate acid is mixed in powder form and under anhydrous conditions with a solid base such as sodium acetate. In this case salt formation does not occur during the process, but rather when the granule is added to water in the spray tank before use.        
“Monsanto do Brasil LTDA” in Brazil sells Roundup WG—this product contains 792.5 g/kg of glyphosate mono-ammonium salt, which is equivalent to 72% glyphosate ae. Most granular glyphosate formulations sold in Brazil, Canada, Australia and USA have loadings of 700 or 680 g/kg ae.
There is an ongoing need for fully formulated granular glyphosate compositions that comprise high loadings of glyphosate.
WO 2007/143788 (Pentland and Flynn, “Herbicidal Composition and Method for Removing Unwanted Foliage”) describes a 2-pack method of preparing a spray tank mix of glyphosate comprising (a) providing glyphosate acid solid concentrate (glyphosate 95% pure, concentrate comprises 950 g/kg acid equivalent); (b) an alkaline composition and (c) adding the glyphosate acid concentrate to a diluted aqueous mixture of the alkaline composition. Whilst the glyphosate acid equivalent loading in one of the packs is very high (950 g/kg), the following constraints arise: (i) the second pack must comprise alkali and will generally comprise liquid alkali (probably in admixture with a glyphosate-synergising surfactant)—the requirement to transport acid and alkaline packs in close proximity is problematic; (ii) the requirement for the glyphosate-synergising surfactant to be compatible with the alkaline material can be problematic, and can limit the suitable glyphosate-synergising surfactants that can be used in the second pack; (iii) the order of addition of the 2 packs is critical for successful application of glyphosate; (iv) the rate of addition of the glyphosate concentrate is critical for successful application of glyphosate—in particular if the glyphosate concentrate is added too rapidly to the diluted alkaline spray water, some of the concentrate may accumulate on the bottom of the spray tank and may not be properly neutralised.
There is also an ongoing need for a 2-pack glyphosate formulation wherein the glyphosate acid-containing pack is at high loading, and wherein the order of addition of the packs to the spray water is not critical.